Rotatable member with an annular groove for dynamic balancing during rotation

ABSTRACT

A rotatable member is adapted for dynamic balancing by the addition of balancing weights in the form of high speed projectiles fired at the member during rotation in timed relationship with the rotation of the member so as to impact the member at specific circumaxial locations required for balancing the member. The member has an annular groove for receiving the projectiles and securing the same at the desired locations. The groove has a cross sectional configuration slightly smaller than that of the projectile in at least one direction of measurement so as to engage and capture the projectile in retention in the groove.

BACKGROUND OF THE INVENTION

Manual dynamic balancing of rotatable members is still a common practice with the member being rotated to determine the points of unbalance, the rotation stopped to attach weights manually, and the member perhaps rotated a second time to check the balance. Obviously, this is a tedious and time-consuming procedure. Attempts at automation have not been widely successful.

U.S. Pat. No. 2,432,659 to Criswell first determines the locations requiring added weight and then sprays “small particles of metal” repeatedly until the member is balanced.

U.S. Pat. No. 2,937,613 discloses firing a “Body” at a groove in a rotating member but does not disclose any means for capturing and retaining the “Body”.

U.S. Pat. No. 3,968,769 to Gusarov et al projects glue onto the circumaxial locations requiring balancing.

U.S. Pat. No. 5,992,232 to Saitoh ejects a liquid balancing agent, which requires curing.

Provisional Patent Application entitled Method and Apparatus for Balancing Fan and Blower Assemblies, filed of even date herewith, discloses a system similar to the foregoing patents but which fires projectiles of metal or the like at a rotating member for balancing the same. The system is highly efficient but requires a means of capturing the projectiles and positively retaining the same at the desired circumaxial locations.

The foregoing patents as well as the Provisional Application are hereby incorporated herein by reference.

It is the general object of the present invention to provide projectile capturing and retaining means on a rotating member in a simple and efficient manner.

SUMMARY OF THE INVENTION

In fulfillment of the foregoing object and in accordance with the present invention, an annular groove is provided in a member to be balanced and has a cross sectional configuration slightly smaller than that of the projectile at least after impact in at least one direction of measurement so as to engage and capture the projectile for retention in the groove. The groove may retain the projectile frictionally or, preferably, the projectile may be retained by positive engagement of the groove wall therewith. This condition may result from a groove design wherein the mouth of the groove is narrower than the interior with at least one mouth-defining portion of the groove wall being flexible for entry of the projectile to the interior of the groove. Preferably, the side of the mouth opposite the flexible portion is inclined from the line of flight of the projectile in the range of 10 to 55 degrees whereby to direct errant projectiles into the groove, and more specifically approximately 30 degrees. Once the projectile has entered the groove, the flexible portion of the groove wall engages and positively clamps the same therein. Alternatively, positive retention of a projectile in a groove may be provided for with a relatively soft projectile, which expands on impact within a groove so as to become larger than the mouth of the groove.

Once captured in a groove it is of course important that unintended or accidental circumaxial movement of the projectiles along the groove be positively prevented. To meet this need, small transverse ribs are provided in a spaced circumaxial series and one or more ribs may be partially deformed on impact whereby to provide the necessary retention of the projectiles at the specific locations required for balancing the rotatable member.

Examples of rotatable members which can be advantageously balanced with the aid of a balancing groove of the invention are air impellers and small electric motors. Centrifugal air impellers and small permanent magnet D.C. motors are specifically discussed herein below.

Finally, a method of balancing employing projectiles fired at rotating members is also discussed below.

DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings illustrates a centrifugal air impeller partially in section provided with a pair of balancing grooves in accordance with the invention.

FIG. 2 is an enlarged fragmentary top view partially in section of a balancing groove.

FIG. 3 is an enlarged cross sectional view of a balancing groove with a projectile in flight and about to enter the groove.

FIG. 4 is an enlarged fragmentary longitudinal section of a groove showing a plurality of transverse ribs engaging and retaining a projectile against movement along the groove.

FIG. 5 is an enlarged fragmentary cross sectional view of a groove and projectile of an alternative embodiment of the invention.

FIG. 6 is a view of still another embodiment of the invention.

FIG. 7 is a view in partial cross section of a small electric motor provided with a pair of balancing grooves.

FIG. 8 is a fragmentary perspective view of a centrifugal air impeller having a specific blade, end ring and back plate construction and which is provided with a balancing grooves in its end ring and backplate.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring particularly to FIG. 1, it will be observed that a centrifugal air impeller indicated generally at 10 is provided with a pair of annular balancing grooves 12 and 14 respectively in end ring 16 and back plate 18. Parallel circumaxially spaced longitudinally extending air moving blades 20, 20 interconnect the end ring 16 and the back plate 18. The grooves 12 and 14 may be identical in construction and are best illustrated in FIGS. 2 and 3.

Referring particularly to FIG. 3, it will be observed that the mouth of the groove 14 at A is somewhat narrower than the interior. A left hand wall portion or lip 22 would tend to block entry of a projectile larger than A but is flexible so as to bend leftwardly sufficiently to allow the projectile to pass and assume the broken line position in the interior of the groove as shown. In the broken line position the projectile is engaged by the lip as it returns to its normal position and a clamping force is exerted by the lip on the projectile urging it against the opposite wall of the groove. Thus, the projectile is captured and positively retained in the groove.

Still referring to FIG. 3, the wall portion 21 of the groove opposite the lip 22 is shown inclined toward the interior of the groove at an angle with the line of flight of the projectile. The purpose of this inclined portion is to direct errant projectiles into the groove and the angle of inclination from the projectile line of flight should fall in the range of 10 to 55 degrees. Preferably the angle should be approximately 30 degrees. It should also be noted that the lip 22 has a shallow arcuate surface 26 facing inwardly so as to be engaged by projectiles causing the lip to flex outwardly and opening the mouth for projectile entry.

Further in accordance with the present invention, ³anti-rotation² ribs 28,28 are provided to retain projectiles in the groove against accidental or inadvertent movement along the groove. As best illustrated in FIGS. 3 and 4, a plurality of ribs 28, 28 are provided in circumaxially spaced relationship along the base of each groove. A projectile such as 24 in FIG. 4 may partially crush a single rib as shown or it may rest between two ribs perhaps partially crushing each. In either event the projectile is restrained against movement along the groove.

In the embodiment of the invention thus far described, the air impeller and thus the balancing groove are of molded plastic construction and the projectile is of metallic construction, the latter actually taking the form of a conventional BB of the type fired from a child's toy rifle. Alternatively, both elements may be of metallic construction or, as will be seen, a relatively soft material may be employed for the projectile and a somewhat harder material for the groove wall.

FIG. 5 illustrates an alternative embodiment of the invention wherein a relatively soft material such as plastic or lead is used for the projectile 24 a and a somewhat harder material such as steel is used for the groove walls 30. The projectile in this instance should be slightly smaller than the mouth A of the groove 14 a. Thus, the projectile freely enters the groove and on impact with the rear wall of the groove deforms slightly so as to flatten somewhat and engage the side walls of the groove which are inclined to make the rear of the groove wider than its mouth. As will be apparent, the projectile is thus captured and positively held in the groove at the desired location. A series of small ribs 32,32 may be provided as above to retain the projectile in position circumaxially.

A further alternative embodiment of the invention is shown in FIG. 6. A groove 14 b has walls 34,34 which incline inwardly from the mouth of the groove to engage a projectile with progressively greater force as it proceeds into the groove. This of course results in a substantial frictional retaining force against withdrawal of the projectile from the groove. To enhance this retaining force small longitudinally extending ribs 36, 36 may be provided on the sidewalls 34, 34. The ribs may be slightly deformed by the projectile to provide a hybrid frictional and positive retention of the projectile.

A further application of balancing grooves is illustrated in FIG. 7. Small electric motor 40 which may be of the permanent magnet DC type, has an external rotor 42 and a stator 44. Depending on the axial dimension of the rotor, one or two balancing grooves may be required. As shown, two grooves 46,48 are provided at opposite sides of the rotor and face in opposite directions. The grooves 46, 48 may be identical and they may also be identical with the above-described grooves 12 and 14 on the air impeller of FIG. 1.

FIG. 8 illustrates the application of balancing grooves to a specific design of a centrifugal air impeller fully disclosed in U.S. patent application entitled IMPROVED INJECTION MOLDED CENTRIFUGAL AIR IMPELLER filed Oct. 31, 2003, hereby incorporated herein by reference. The impeller design emphasizes the provision of a mold parting line at an intermediate longitudinal portion of blades 45,45 as shown by the broken Line 46. Balancing grooves 49, 50 are provided respectively at end ring 52 and back plate 54 and may be identical with the grooves of FIG. 1. The end ring 52 is considerably enlarged relative to the end ring of the aforementioned patent application to accommodate the balancing groove 49.

Finally, the general method of balancing a rotating member as set forth in the aforementioned patent applications and the Provisional application incorporated herein by reference is greatly enhanced by the addition of a balancing groove. Thus, an improved method in accordance with the invention comprises providing an annular balancing groove in a member requiring balancing, determining a location where a balancing weight is needed, firing a projectile in timed relationship with the rotation of the member so that the projectile enters the groove at the 

1. A rotatable member adapted for dynamic balancing by the addition of balancing weights in the form of high-speed projectiles fired at the member during rotation in timed relationship with the rotation of the member so as to impact the member at specific circumaxial locations required for balancing of the member, said member having an annular groove for receiving projectiles and securing the same at the desired locations for balancing the member, the wall of the groove having a cross sectional configuration approximating that of a projectile but slightly smaller than that of the projectile at least after impact in at least one direction of measurement so as to engage and capture the projectile for retention in the groove.
 2. A rotatable member as set forth in claim 1 wherein the groove is configured and dimensioned to retain the projectile frictionally.
 3. A rotatable member as set forth in claim 1 wherein the groove is configured and dimensioned to retain the projectile by positive engagement therewith.
 4. A rotatable member as set forth in claim 1 wherein the mouth of the groove is narrower than that of the interior with at least one mouth defining wall portion thereof being flexible for entry of the projectile to the interior of the groove.
 5. A rotatable member as set forth in claim 4 wherein one side of the mouth of the groove takes the form of a flexible lip and the other side is rigid, the lip flexing to allow entry of the projectile.
 6. A rotatable member as set forth in claim 5 wherein said other side of the groove wall is inclined from the line of flight of the projectile in the range of 10 to 55 degrees whereby to direct errant projectiles into the groove
 7. A rotatable member as set forth in claim 6 wherein the angle of inclination of the groove wall is approximately 30 degrees.
 8. A rotatable member as set forth in claim 5 wherein the groove is so configured and dimensioned that the lip engages the projectile after entry and exerts a clamping force to positively retain the projectile in the groove.
 9. A rotatable member as set forth in claim 1 wherein a series of small transverse ribs are provided in the groove and are spaced circumaxially so as to engage projectiles in the groove and secure them against accidental or inadvertent movement circumaxially along the groove.
 10. A rotatable member as set forth in claim 9 wherein the ribs are of a material somewhat softer than that of the projectile so as to be at least partially crushed by the latter.
 11. A rotatable member as set forth in claim 1 wherein the projectile is spherical and the groove is at least partially cylindrical.
 12. A rotatable member as set forth in claim 1 wherein the member is of molded thermoplastic construction and the projectile is of metallic construction.
 13. A rotatable member as set forth in claim 1 wherein both the member and the projectile are of metallic construction.
 14. A rotatable member as set forth in claim 3 wherein the projectile is of a relatively soft material so as to expand on impact with the rear wall of the groove for retention in the groove.
 15. A rotatable member as set forth in claim 14 wherein the projectile is of a metal such as lead.
 16. A rotatable member as set forth in claim 1 wherein the member takes the form of a centrifugal air impeller having a back plate residing in a radial plane, a circumaxially spaced series of longitudinal air moving blades extending axially there from and an end ring supporting the blade end portions opposite the back plate, and wherein the groove is formed in the inlet ring.
 17. A rotatable member as set forth in claim 16 wherein the groove is formed in the back plate.
 18. A rotatable member as set forth in 16 wherein grooves are formed in both the end ring and back plate.
 19. A rotatable member as set forth in claim 1 wherein the member takes the form of a rotor of an electric motor and wherein at least one groove is formed in the rotor.
 20. A rotatable member as set forth in claim 19 wherein a pair of grooves are provided in the rotor in axially spaced relationship and facing in opposite axial directions.
 21. A plastic injection molded centrifugal air impeller comprising a circumaxially spaced series of air moving blades each having inner and outer edges and longitudinally extending inner and outer portions on opposite sides of an intermediate longitudinal line, an end ring at the inlet end of the impeller formed integrally with and interconnecting the blades, said ring having an inner diameter greater than that of the blades inner edges and an outer diameter greater than that of the blade outer edges, and said ring also having a balancing groove with a cross sectional configuration adapted to receive and retain a balancing projectile, and a back plate formed integrally with and interconnecting the blades at an end opposite the inlet ring, the diameter of the back plate being at least equal to that of the inner edges of the blades, and the forgoing characteristics of the impeller accommodating the molding of the blade inner portions in the core of a plastic injection mold and the molding of the blade outer portions in the cavity of the mold.
 22. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the diameter of the back plate is larger than that of the inner edges of the blades
 23. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the blades are notched to receive an inner edge portion of the end ring.
 24. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the end ring extends axially beyond the ends of the blades.
 25. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the blades have rounded inner edges.
 26. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the blades are forwardly curved.
 27. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the outer portions of the blades are thinner than the inner portions thereof.
 28. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the inner diameter of the inlet ring is approximately 1 to 7 per cent less than that of the outer edges of the blades.
 29. A plastic injection molded centrifugal air impeller as set forth in claim 21 wherein the inner diameter of inlet ring is approximately 2 to 5 per cent less than that of the outer edges of the blades.
 30. A method for balancing a rotating member comprising the steps of providing an annular balancing groove in the member which is configured to receive and retain a balancing projectile; determining a circumaxial location where a balancing weight is required, firing a balancing projectile in timed relationship with the rotation of the member so that the projectile enters the groove at the predetermined location which requires a balancing weight, repeating the foregoing steps as required to cure additional points of imbalance.
 31. A method for balancing a rotating member as set forth in claim 30 wherein the annular groove is provided with a mouth narrower than its interior and with at least one mouth defining wall portion being flexible for entry of the projectile to the interior of the groove.
 32. A method for balancing a rotating member as set forth in claim 30 wherein a flexible lip is provided at one side of the mouth of the groove and the groove is so configured and dimensioned that the lip engages the projectile after entry and exerts a clamping force to positively retain the projectile in the groove. 